On 11/26/22 14:41, Shawn Heisey wrote:
The GC log analyses below cover a full index rebuild on OpenJDK 11:

G1GC:
https://www.dropbox.com/s/rvw27xlanlmydry/gc_analysis_g1gc.png?dl=0

ZGC:
https://www.dropbox.com/s/rl80tnf4x1x9wjh/gc_analysis_zgc.png?dl=0

Focusing on one part of the full GC reports above:

https://www.dropbox.com/s/qorl9x0doywxqhy/total_time_g1gc.png?dl=0
https://www.dropbox.com/s/qs4r3aznspb4pub/total_time_zgc.png?dl=0

For this tiny index, G1GC spends a lot less time doing concurrent tasks than ZGC, but has about twice as much pause time.  The difference in concurrent time on this system is VERY significant. This instance only has two CPUs, so there's not a lot of CPU power to handle concurrent threads.  Having over a minute of concurrent GC time (compared to about 3 seconds with G1GC) resulted in the rebuild time increasing by three minutes.

I think that with a very large heap and/or a large number of CPU cores, ZGC will completely trounce G1GC.   Further testing on large installs that I don't have is required.

Thanks,
Shawn


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